Simple Solutions That Work! Issue 18

bellows is retracted to a physical stop with valve to the inlet to the resin storage open, it is filled completely. To meter the liquid into the mixer, the discharge valve is opened and the bellows is compressed at a controlled rate to a physical stop. This very simple and repeatable process results in extremely accurate liquid delivery to every batch time after time. The system can be configured to deliver the 2 resins at the same time, or one after the other. A controlled rate of addition is critical to eliminate the potential for resin saturation, resin balls, and streaking. The liquid is introduced into the chamber by going through on the mixing blade components. This results in 100% of the expensive chemicals being used and practically eliminates post flow which helps lessen resin buildup on the chamber lining. As a result, the mix is consistent, batch times are reduced, maintenance time is reduced and the need to clean the chamber and mixing mechanism is also lessened. VIBRATORY MIXERS While not as well-known, vibratory mixers are the ultimate in simplicity. This design is very popular with high production automotive foundries where they have been tested extensively and proven to be exceptional in the areas of tensile strength, ease of calibration, cleaning, and resin efficiency. While traditionally produced in smaller sizes, larger mixer designs are readily available. The vibratory mixer is comprised of a cannister with internal flighting clamped to an isolated mechanical structure equipped with a high-speed vibrator opposite the cannister. The resin metering system is identical to the horizontal shaft mixer with the inherent durability, accuracy, and repeatability. The sand is metered into the cannister with the above- described timed hopper. When the vibrator starts, the sand flows around the carefully engineered and extremely durably flighting. This process results in a very evenly coated sand with minimal resin additions. Once the mix cycle times out, the stopper in the bottom of the cannister opens while the vibrator is still running. The sand flows out of the cannister very quickly, closes, and is then immediately ready to be refilled. CONTINUOUS MIXERS While not as popular as batch mixers for modern no-bake core machines, continuous mixers are gaining in popularity for a variety of attractive reasons. The cost of a modern high speed continuous mixer is much less than others in a per lb produced / time ratio, and are more flexible. The amount of sand produced per minute is very repeatable as it is a simple matter to set the amount of time needed to produce the required amount of sand. Mixing efficiency has been proven to be better than S-blade mixers, and are much faster assuming the mixer is correctly sized. The resin is metered into the mixing chamber with traditional close tolerance spur gear pumps and the pumps are magnetically coupled to eliminate resin leakage on the newer machines. The level sensor in the hopper above the core machine blow chamber valve tells the mixer to run and for how long. There is an age-old controversy that states that the only way to get the exact same sand in a given amount is with a batch mixer. While this used to be true years ago, with today’s accurate drive motors, valves and pumping systems, this is no longer a concern (much less a controversy). A properly designed PLC, pumping system, diverter, valving, ensures that the resin can be delivered to meet the sand at the exact moment the sand is at the resin ports. It can also immediately cease delivery when the sand stops, resulting in the correct amount of resin being metered into the chamber, at the correct time. Continued on next page 41 HOW TO ISSUE